This invention relates to radar systems that transmit a pulsed beam of high frequency energy into a predetermined volume of space in a scanning mode to identify the presence, locus, motion, and characteristics of scatters in the predetermined region of space.
It is a problem in the field of radar systems, and weather radar systems in particular, to implement an inexpensive system that collects sufficient data to provide accurate information to the users relating to the presence, locus and characteristics of scatters in a region of space, in a short period of time. Radar systems can be characterized in terms of the basic system architecture as either monostatic radar systems which use a single transmitter and receiver or bistatic radar systems which use a single radar transmitter and a plurality of receivers, at least one of which is located remotely from the transmitter site.
Included in the field of monostatic radar systems are the standard narrow beam radar systems which transmit a single narrow beam of high frequency radiation, then receive signals, which constitute components of this narrow beam that have been reflected off scatterers located in the path of the beam. These systems usually include a mechanically driven antenna to execute a predetermined scan pattern that covers a predetermined volume of space. The scanning speed is limited by the ability to obtain independent meteorological samples using a single frequency and by the ability to mechanically move a large antenna, thereby preventing these systems from both scanning extremely rapidly and frequently revisiting particular regions of space. To increase the accuracy of the data produced by the narrow beam radar systems, expensive rotating high gain antennas are used. As a result, the cost of implementing, operating, and maintaining such systems is high. Furthermore, the accuracy of the data produced is adversely affected by the infrequent scan pattern of the rotating antenna. These narrow beam radar systems, when used as a weather radar, collect data that is indicative of only the radial component of the wind field present in the predetermined volume of space. To compensate for this limitation, it is common to use multiple radars to collect data, but in these radar networks, users have to wait for a volume update to be completed before data is available for use. In the most common radar networks, such as the USA WSR-88D Weather Service Network, these volume updates require up to 6 minutes. Thus, weather data is not available in a timely manner using existing radar networks.
An alternative to monostatic radar systems are the bistatic radar networks which use a single radar transmitter and a plurality of passive, low-gain receivers, at least one of which is located remotely from the transmitter site, such as is disclosed in U.S. Pat. Nos. 5,410,314, 5,469,169, 5,471,211. In such a network, the transmitter produces a xe2x80x9cpencil beamxe2x80x9d of high frequency energy, which is reflected off scatterers as the rotating antenna scans the predetermined volume of space. The reflected radial component of the beam is received by a receiver located at the transmitter site, while other components of the reflected beam are received at other receivers located remote from the transmitter site. The bistatic radar network has the advantage of receiving back scattered reflections indicative of the radial component of the scatterer motion as well as other components, which enable the network to simply produce a three-dimensional determination of the characteristics of the scatterers. This radar network is relatively inexpensive due to the use of the plurality of passive, low-gain receivers, but does require the use of a transmitter that is closely synchronized with the plurality of remotely located receivers to enable the receivers to track the transmitted pulses by working from the same time base and scan pattern as the transmitter. The synchronization can be accomplished on a less than pulse basis, if the transmitter frequency, pulse rate and scan pattern are all known and immutable. However, any irregularities in these criteria result in the receivers being incapable of computing the location of the scatterers, since the origin of the pulses are not known.
The above described problems are solved and a technical advance is achieved by the present bistatic radar system for centralized, near-real-time synchronized, processing of data to identify scatterers in a predefined space. The bistatic radar system uses a scanning beam antenna located at the transmitter to transmit a focused beam of high frequency energy into a predefined space, with the transmitted beam comprising a series of pulses. The transmitter also includes apparatus for determining pulse origination data comprising: pulse origination time and direction of propagation for each of the pulses in the transmitted beam emanating from the antenna, where the antenna is scanned in a predetermined scan pattern in at least an azimuthal direction. The bistatic radar system also includes at least one receiver, located at a site remote from the transmitter and includes apparatus for generating pulse component receipt data indicative of receipt of components of the pulses that are contained in the transmitted beam that are reflected from scatterers in the predefined space. The receivers all transmit their data as received back to a central processor, which synchronizes (collates) the data in order to calculate, in near real-time, vector wind fields, divergence, vorticity, etc. These calculations typically are performed in polar coordinates or can be performed in Cartesian coordinates. Thus, the present bistatic radar system performs near-real-time synchronization, collating, transmission, and processing of data received from one or more bistatic receivers and from a transmitting radar to produce weather data in a more timewise efficient manner.